1. Field of the Invention
The present invention relates to a vibration isolator for mounting a vibrating body on a structural body.
2. Description of the Prior Art
For mounting vibrating bodies such as engines on structural bodies such as automobile chassis, there have heretofore been widely employed vibration isolators each composed of two attachment members joined respectively to the vibrating body and the structural member and a resilient block of rubber fixed to the attachment members to couple them. In the conventional vibration isolator of the above type, the resiliency of the rubber block serves as a spring for absorbing shocks and the internal friction of the rubber block due to yielding thereof serves as a damper for dissipating the energy of vibration. The vibration isolator is required to be designed with a view to both reducing vibrations transmitted to the structural body and supporting the vibrating body securely on the structural body, dependent on the static load to be borne and the intensity and the frequency of vibrations of the vibrating body.
It is relatively easy to design a vibration isolator if the frequency of vibrations of the vibrating body is constant or in a narrow range. However, in the event that the vibration frequency varies normally in a wide range, it has been difficult to design a vibration isolator capable of sufficiently isolating all vibrations in the wide frequency range. For example, a four-cylinder four-stroke automotive engine normally operating in a range of from about 600 r.p.m. to 6,000 r.p.m. vibrates in a frequency range of from about 20 Hz to 200 Hz. Any vibration isolators conventionally available for mounting such an automotive engine have proven satisfactory in isolating engine vibrations merely in a portion of the above frequency range.